Chapter 4.1

1.Continental Drift a.A hypothesis stating that the continents once formed a single landmass, broke up, and drifted to their present locations. b.Proposed by a German Scientist named Alfred Wegener.

c.Pangaea i.The name that Wegener gave to the solid land mass formed by all continents. ii.It means “all lands”.

e.Panthalassa i.The name that Wegener gave to the single ocean that surrounded Pangaea. ii.It means “all seas”.

225 MYA200 MYA 150 MYA 65MYA PRESENT DAY

a.Wegener hypothesized that Pangaea began breaking up during the Mesozoic Era and forming our current landmasses we know as continents. b.He also believed this motion crumpled the land in areas forming mountains.

2.Continental Drift Evidence a.The edges of our current continents fit together much like a puzzle. b.Fossils of the same land animals, from 270 million years ago, have been found in Eastern South America and Western Africa. It would have been impossible for these animals to swim across the Atlantic Ocean.

c.Geologic evidence of age and type of rocks in the coastal regions of Western Africa and Eastern Brazil match closely. i.Mountain chains that end at the coastline of one continent continue on landmasses across the ocean.

1.The Appalachians extend northward along the eastern United States and mountains of similar age and structure are also found in Scotland and Northern Europe. If these landmasses are observed in Pangaea, they fit together.

i.Coal deposits have been found in the United States, Europe, and Siberia that indicate a subtropical to tropical climate. d.Glacial evidence also proves that Pangaea once existed. i.Glacier debris has been found in Southern Africa and South America, areas that are to warm to have glaciers.

e.While we now know continental drift to be a fact, it was opposed by the scientific world of his time due to the fact that he couldn’t give a reason of force that would move the continents. Wegener died in 1930 and never found a reason.

1.Seafloor Spreading a.This is the evidence that Wegener was searching for to prove his hypothesis of continental drift. b.This is the movement of the ocean floor away from either side of a mid- ocean ridge.

c.A mid-ocean ridge is a system of undersea mountain ranges that wind around the Earth. d.The Mid-Atlantic Ridge is an undersea mountain range with a steep, marrow valley along its center.

d.Due to the spreading of the seafloor, the relative age of the ocean floor is very young compared to the age of the continental rocks. i.The oceanic rocks are no older than 175 million years, while the oldest continental rock is about 4 billion years old.

e.A man named Harry Hess hypothesized the action of seafloor spreading. i.According to Hess, if the seafloor is pulling apart, then it would cause a break, or rift, in the seafloor, which would cause an upwelling of magma from the rift. The magma would eventually solidify and be new seafloor. ii.If the seafloor is spreading at rifts, then it would be possible that the continents are spreading along with it.

a.Paleomagnetism i.The study of the record of the Earth’s magnetism in rocks. ii.Recall that the Earth generates a magnetic field and creates two poles, North and South with opposite polarity.

iii.As magma solidifies to form rock, the magnetic fields of iron-rich minerals align with the Earth’s magnetic field, similar to a compass. 1.When the rock hardens, the orientation of the minerals are permanent and point north.

a.Paleomagnetism as Evidence i.Scientists have discovered bands of minerals that do not point North, as they should. ii.This discovery shows that the Earth’s polarity has reversed itself numerous times in history (North is South, and South is North).

iii.They have also discovered that these bands are similar on either side of an ocean rift and are dated during the same period of polarity. 1.Being able to date bands of minerals by their polarity on either side of an ocean rift is proof of sea floor spreading.

2.Scientists have also discovered a band on continental rock that matches a band on the opposite side of an ocean rift and is in the ocean. This is further proof of continental drift.